The invention generally relates to the field of electric components, and is preferably to be applied in designing the configuration of vacuum interrupters. More preferably, it relates to vacuum interrupters in which at least one of the two contacts has an inner contact region which projects axially over an outer contact region serving the purpose of arc quenching.
Vacuum interrupters with contact arrangements of the type are known. In this case, the two contacts, of which, generally speaking, only one can be moved axially relative to the other, are fitted with circular or slightly conical contact surfaces which face one another. Contacts which are constructed as what are termed xe2x80x9cvane/blade electrodesxe2x80x9d or xe2x80x9cspiral contactsxe2x80x9d have an inner contact region provided for switching operating currents, and an outer contact region, which surrounds the inner contact region concentrically, is provided for interrupting short-circuit currents and serves as running surface for a rotating arc. In this case, the inner contact region projects over the outer contact region by a certain, not very large amount (U.S. Pat. Nos. 3,158,719 A, 3,809,836 A).
Vacuum interrupters are also known in which the contact region provided for switching operating currents is identical with the contact region provided for interrupting the short-circuit currents. These contacts are of cup-shaped construction, the wall of the cup and, if appropriate, also the contact ring mounted on the top edge being provided with a plurality of slits which run obliquely relative to the longitudinal axis of the contact arrangement. The contact surface can be subdivided into a plurality of contact subsurfaces by means of these slits (DE 23 21 753 A1, DE 29 12 823 A1).
In order to be able to separate welded contact regions more easily from one another in the case of vacuum interrupters, it is known to give each contact a relatively large number of contact surfaces and to hold these elastically on a main contact body. A tubular main contact body can be provided for this purpose with radially inwardly projecting support arms for the contact surfaces (U.S. Pat. No. 3,869,589 A).
Furthermore, for air-switching circuit breakers in the low-voltage field it is known per se to split up the movable contact into a plurality of contact fingers arranged parallel to one another, for the purpose of reducing the contact pressure force (U.S. Pat. No. 5,210,385 A).
In vacuum interrupters for circuit breakers, in particular for circuit breakers in the low-voltage field (for example U.S. Pat. No. 5,661,281), the high currents give rise to high forces on the contacts which tend to raise the contacts off one another. These current forces must be compensated by means of suitable measures so that the contacts do not lift off with the risk of them becoming welded to one another. In the case of switches fitted with vacuum interrupters, this problem has been solved so far by making use, in addition to a permanently applied static contact pressure force, of an additional current loop with the aid of which high dynamic magnetic field forces which act to strengthen the contact force are produced in the short term, that is to say particularly during the occurrence of short circuit currents. There is no need thereby for mechanical application of the entire contact pressure force, which is required only in the short term. Because of the relatively high costs of such current loops, the contact force to be mechanically applied in a permanent fashion continues, however, to be relatively large and can be several kN per switching pole, particularly in the case of high currents of more than 50 kA. This requires a correspondingly high mechanical outlay in the switching device.
Starting from a contact arrangement having the features of the preamble of patent claim 1, it is an object of the invention to construct the contact arrangement such that the mechanical contact point is distributed over a plurality of separate individual contacts with a defined spring constant, and that an arc can nevertheless rotate.
In order to achieve this object, for example, it is provided according to the invention that the inner contact region including a plurality of contact subregions arranged next to one another on a divided circle, each contact subregion being formed by the free end of a resilient contact tongue inclined relative to the axis of the contact arrangement.
Such a configuration of the contact arrangement permits the contact region provided for switching operating currents to be broken down into a larger number of, for example, three to ten subregions and for these subregions to be constructed as resilient contact tongues opposite which there is a mating contact piece in each case, and to decouple the contact tongues so far from one another mechanically by appropriate dimensioning of the spring constant that in the closed state of the contact arrangement all the subregions are subjected to a contact pressure force of the same magnitude. The resilient contact tongues can be arranged in this case such that upon opening and closing of the contact system a frictional movement is avoided, and thus so is abrasion in the form of metallic chips.
In order to have sufficient space to configure the dimensioning of the spring constants of the contact tongues, the contact tongues can be produced from a flat, conical shell by multiply slitting the shell wall in an axial fashion. In this case, the spring constant can be varied, in particular, by the thickness of the shell wall and the number of the slits and/or the width of the contact tongues. Similar relationships are obtained when the contact tongues are produced from a flat, hollow conical frustum by multiply slitting the conical lateral surface in an axial fashion.
In a way resembling the configuration of the slit contact carrier of what are termed cup-shaped contacts, the contact tongues can also be produced from a tube length by providing the wall thereof with a plurality of obliquely running slits.
The design configuration described for the contact tongues can be applied both in the case of spiral contacts and in the case of cup-shaped contacts. The body used for the contact tongues can include, in this case of dispersion-hardened copper, a specific copper alloy or a copper/chromium material with a small proportion of chromium. It is fabricated separately and arranged in the middle of the respective contact in an appropriate cutout and soldered to the remaining contact body.